1. Field of the Invention
This invention relates to a radiation image recording and read-out apparatus for exposing individual stimulable phosphor sheets to a radiation passing through an object to have a radiation image of the object stored thereon, exposing the individual stimulable phosphor sheets to stimulating rays which cause them to emit light in proportion to the stored radiation energy, and detecting and converting the emitted light into electric signals. This invention particularly relates to a radiation image recording and read-out apparatus in which the stimulable phosphor sheets are conveyed by a circulation and conveyance means along a predetermined circulation path in the apparatus and circulated and reused for recording radiation images.
2. Description of the Prior Art
When certain kinds of phosphors are exposed to a radiation such as X-rays, .alpha.-rays, .beta.-rays, .gamma.-rays, cathode rays or ultraviolet rays, they store a part of the energy of the radiation. Then, when the phosphor which has been exposed to the radiation is exposed to stimulating rays such as visible light, light is emitted by the phosphor in proportion to the stored energy of the radiation. A phosphor exhibiting such properties is referred to as a stimulable phosphor.
As disclosed in U.S. Pat. Nos. 4,258,264, 4,276,473, 4,315,318 and 4,387,428 and Japanese Unexamined Patent Publication No. 56(1981)-11395, it has been proposed to use a stimulable phosphor in a radiation image recording and reproducing method. Specifically, a sheet provided with a layer of the stimulable phosphor (hereinafter referred to as a stimulable phosphor sheet) is first exposed to a radiation passing through an object such as the human body to have a radiation image of the object stored thereon, and is then scanned with stimulating rays which cause it to emit light in proportion to the stored radiation energy. The light emitted by the stimulable phosphor sheet upon stimulation thereof is photoelectrically detected and converted to electric image signals, which are processed as desired to reproduce a visible image having an improved quality, particularly a high diagnostic efficiency and accuracy. The finally obtained visible image may be reproduced in the form of a hard copy or may be displayed on a cathode ray tube (CRT). In this radiation image recording and reproducing method, the stimulable phosphor sheet is used to temporarily store the radiation image in order to reproduce the final visible image therefrom on a final recording medium. For economical reasons, therefore, it is desirable that the stimulable phosphor sheet be used repeatedly.
Further, in a mobile X-ray diagnostic station such as a traveling X-ray diagnostic station in the form of a vehicle like a bus which is provided with a radiation image recording and read-out apparatus for carrying out the aforesaid radiation image recording and reproducing method and moves from place to place to record radiation images for mass medical examinations, it is disadvantageous to load the mobile X-ray diagnostic station with a large number of stimulable phosphor sheets, and the number of the stimulable phosphor sheets which can be loaded on the mobile X-ray diagnostic station is limited. Therefore, it is desired to load the mobile X-ray diagnostic station with stimulable phosphor sheets which can be used repeatedly, once store the radiation images of the objects respectively on the stimulable phosphor sheets, transfer the electric image signals read out from the stimulable phosphor sheets to a recording medium having a large storage capacity, such as a magnetic tape, and circulate and reuse the stimulable phosphor sheets for further image recording and read-out operations, thereby to obtain the radiation image signals of many objects. Further, when image recording is conducted continuously by circulating and reusing the stimulable phosphor sheets, it becomes possible to increase the image recording speed in mass medical examination. This is very advantageous in practical use.
In order to reuse stimulable phosphor sheets as described above, the radiation energy remaining on the stimulable phosphor sheet after it is scanned with stimulating rays to read out the radiation image stored thereon should be erased by a method as described in, for example, U.S. Pat. No. 4,400,619 or Japanese Unexamined Patent Publication No. 56(1981)-12599. The stimulable phosphor sheet should then be used again for radiation image recording.
From the aforesaid viewpoint, the applicant proposed in Japanese Unexamined Patent Publication No. 59(1984)-192240 a built-in type radiation image recording and read-out apparatus comprising:
(i) an image recording section for recording a radiation image of an object on a stimulable phosphor sheet by exposing the stimulable phosphor sheet to a radiation passing through the object,
(ii) an image read-out section provided with a stimulating ray source for emitting stimulating rays for scanning the stimulable phosphor sheet carrying the radiation image stored thereon at the image recording section, and a photoelectric read-out means for detecting light emitted by the stimulable phosphor sheet scanned with the stimulating rays to obtain electric image signals, and
(iii) an erasing section for, prior to the next image recording on the stimulable phosphor sheet for which the image read-out has been carried out at the image read-out section, having the stimulable phosphor sheet release the radiation energy remaining on the stimulable phosphor sheet, whereby the stimulable phosphor sheet is conveyed by a circulation and conveyance means, circulated through the image recording section, the image read-out section and the erasing section, and reused for radiation image recording.
The proposed built-in type radiation image recording and read-out apparatus is suitable for loading on a mobile X-ray diagnostic station such as a traveling X-ray diagnostic station in the form of a vehicle like a bus for the purpose of mass medical examinations or the like.
Besides the case where the aforesaid radiation image recording and reproducing method is carried out by use of the built-in type radiation image recording and read-out apparatus as mentioned above, the radiation image recording and reproducing method is often carried out by recording a radiation image on a stimulable phosphor sheet by use of an image recording apparatus for conducting only the image recording, taking the stimulable phosphor sheet out of the image recording apparatus, feeding the stimulable phosphor sheet to an image read-out apparatus independent from the image recording apparatus, and reading out the radiation image stored on the stimulable phosphor sheet. In the latter case, the stimulable phosphor sheet is subjected to image recording in the image recording apparatus in the form housed in a radiation-permeable, lighttight cassette for housing a single stimulable phosphor sheet therein, thereafter fed to the image read-out apparatus in the form housed in the cassette, taken out of the cassette in the image read-out apparatus, and sent to an image read-out zone for carrying out image read-out.
In the case of the conventional built-in type radiation image recording and read-out apparatus, the stimulable phosphor sheet is circulated through the image recording step, the image read-out step and the erasing step in the apparatus, and therefore is not housed in a cassette. On the other hand, in the case where image recording and image read-out are carried out by use of an independent image recording apparatus and an independent image read-out apparatus, the stimulable phosphor sheet is first housed in a cassette, subjected to image recording in the image recording apparatus, and fed to the image read-out apparatus in the form housed in the cassette after image recording is finished. Therefore, the stimulable phosphor sheet processed in the built-in type radiation image recording and read-out apparatus and the stimulable phosphor sheet processed in the other type of the apparatus have to be substantially discriminated from each other, and it is not always possible to feed the stimulable phosphor sheet having a radiation image recorded thereon in the image recording apparatus to the built-in type radiation image recording and read-out apparatus and carry out image read-out from the sheet therein, or to take out the stimulable phosphor sheet, on which image recording has been carried out in the built-in type radiation image recording and read-out apparatus, from the built-in type apparatus and feed it to the external image read-out apparatus. Accordingly, it has heretofore been impossible to use the built-in type radiation image recording and read-out apparatus together with the independent image recording apparatus and/or the independent image read-out apparatus and to utilize only the image recording function or the image read-out function of the built-in type radiation image recording and read-out apparatus.